Method of preparing microparticles

Abstract

A method of preparing microparticles comprising an aqueous solution or dispersion of an oil or gas field production chemical encapsulated in a continuous polymeric phase comprising a degradable polymer, which method comprises: (a) preparing a water in oil in water double emulsion or a water in oil in oil double emulsion having an internal aqueous phase comprising an aqueous solution or dispersion of the production chemical and an internal oil phase comprising a solution of a degradable polymer dissolved in a volatile organic solvent wherein the internal aqueous phase is dispersed in the internal oil phase of the double emulsion in the form of droplets having a mean diameter of less than 10 microns; and (b) at least in part evaporating the volatile organic solvent from the double emulsion such that the degradable polymer accumulates around the droplets of the internal aqueous phase and hardens to form microparticles comprising a continuous polymeric phase encapsulating the internal aqueous phase having a mean particle diameter of less than 10 microns.

1 - 31 . (canceled)  
     
     
         32 . A method of introducing an oil or gas field production chemical into a subterranean formation comprising: 
 (a) injecting a suspension comprising microparticles suspended in a liquid medium into a formation through an injection well wherein the microparticles have a mean diameter of less than 1 micron and wherein the microparticles comprise an aqueous phase comprising an aqueous solution of a water-soluble oil or gas field production chemical or an aqueous dispersion of water-dispersible oil gas or gas field production chemical encapsulated in a continuous polymeric phase, and the polymer forming the continuous polymer phase is degradable under the conditions encountered in the formation;    (b) allowing the suspension to percolate through the formation towards a production well; and    (c) controllably releasing the aqueous solution of the water-soluble oil or gas field production chemical or the aqueous dispersion of the water-dispersible oil or gas field production chemical from the microparticles into the formation and/or the production well through degradation of the polymer forming the continuous polymeric phase.    
     
     
         33 . A method as claimed in  claim 32  wherein the microparticles have a mean diameter in the range 100-750 nm.  
     
     
         34 . A method as claimed in  claim 32  wherein the suspension propagates through the formation at a rate of 15 to 100 feet per day.  
     
     
         35 . A method as claimed in  claim 32  wherein the injection well is 0.25 to 1 mile from the production well.  
     
     
         36 . A method as claimed in  claim 32  wherein the suspension is injected down the injection well at a temperature of less than 10° C.  
     
     
         37 . A method as claimed in  claim 32  wherein the microparticles start to release the aqueous solution or aqueous dispersion of the oil or gas field production chemical at a threshold temperature in the range 50 to 150° C.  
     
     
         38 . A method as claimed in  claim 32  wherein the temperature of the injected suspension increases at a rate of 1 to 10° C. per 100 feet in the radial direction from the injection well towards the production well.  
     
     
         39 . A method as claimed in  claim 32  wherein the microparticles release substantially all of the aqueous solution or aqueous dispersion of the oil or gas field production chemical in the near wellbore region of the production well.  
     
     
         40 . A method as claimed in  claim 32  wherein the microparticles are dispersed in the liquid medium in an amount of from 20 to 50% by weight.  
     
     
         41 . A method as claimed in  claim 32  wherein the oil or gas field production chemical is dissolved or dispersed in the internal aqueous phase of the microparticles in an amount in the range of from 1 to 50 percent by weight, preferably 5 to 30 percent by weight.  
     
     
         42 . A method as claimed in  claim 32  wherein the oil or gas field production chemical is selected from the group consisting of water-soluble or water-dispersible (i) scale inhibitors, (ii) corrosion inhibitors, (iii) hydrogen sulphide scavengers and hydrate inhibitors.  
     
     
         43 . A method as claimed in  claim 32  wherein the liquid medium of the suspension is selected from the group consisting of an oil, an organic solvent and water.  
     
     
         44 . A method as claimed in  claim 43  wherein the liquid medium is a water dispersible organic solvent selected from the group consisting of methyl butyl ether, butyl monoglycol ether and biodegradable esters.  
     
     
         45 . A method as claimed in  claim 32  wherein the suspension of microparticles is continuously or intermittently dosed into the injection water.  
     
     
         46 . A method as claimed in  claim 45  wherein the production chemical is a scale inhibitor and the amount of scale inhibitor released into water production from the production well is in the range 1 to 200 ppm.  
     
     
         47 . A method as claimed in  claim 32  wherein the microparticles are microcapsules or microspheres.  
     
     
         48 . A method as claimed in  claim 47  wherein the microcapsules comprise a well-defined core of the aqueous solution of the water-soluble oil or gas field production chemical or of the aqueous dispersion of the water-dispersible oil or gas field production chemical, and a well-defined wall comprising the degradable polymer.  
     
     
         49 . A method as claimed in  claim 47  wherein the microspheres comprise a continuous polymeric matrix comprising the degradable polymer encapsulating the aqueous solution or aqueous dispersion at either a macroscopic or molecular level.  
     
     
         50 . A method as claimed in  claim 49  wherein the polymeric matrix is porous or non-porous.  
     
     
         51 . A method as claimed in  claim 49  wherein a plurality of droplets of the aqueous solution or aqueous dispersion are encapsulated in the polymer matrix.